IMO it would be nice to have a tool that could display arbitrary output, a la WMII's status bar. This could be useful for piping uptime, battery info, etc. to the toolbar. Since the output would be piped into the toolbar, it would be more convenient for system info stuff than a pipe menu; and since it wouldn't require desklets and such, it would save screen real estate.
I'm thinking it could look something like this in ~/.fluxbox/init:
session.screen0.toolbar.tools: workspacename, systemtray, pipeoutput, clock
session.screen0.pipeoutput.command: echo $(uptime) '|' $(acpi -b)
With pipeoutput.command being any command that generates text output, and pipeoutput.upinterval being the time in seconds between updates. Although the clock has an update interval already, so maybe the pipeoutput tool should just use the clock's update interval. (Presumably one second?)
BTW I have some rudimentary knowledge of C++, so if for some reason it's not feasible for the dev team to code this, I may be able to submit my own implementation. If I do, though, don't expect the code quality to be good. :)